The instant invention relates to thermostatic switching devices and more particularly to a cap and bracket assembly for a thermostatic switch and to a method of manufacturing the cap and bracket assembly.
The use of thermostatic switching devices, of the type comprising a housing having a cap portion and a bimetallic actuating disc received in the cap portion, is extremely well known for a wide variety of temperature related switching applications. It is also well known that for many temperature related switching applications, such as in fire alarm systems, the response times of bimetallic disc actuated thermostatic switches must be minimized in order for the systems in which they are applied to effectively perform their intended functions. Further, it is generally known that the response times of bimetallic disc actuated switches can be significantly reduced if they include heat transfer brackets attached to the caps thereof for collecting and/or transferring heat to bimetallic discs thereof which are received in the caps. In most cases, the brackets of switches of this type are assembled with the caps thereof before the caps are assembled with the other components of the switches and they comprise plate or disc-like elements having apertures therethrough. The caps of cap and bracket assemblies of this type are generally of cup-shaped configuration, and they comprise enlarged substantially circular main portions which define the open ends thereof and reduced substantially circular end portions which define the closed ends thereof. Further, the caps of cap and bracket assemblies of this type are preferably dimensioned and configured so that when they are received in assembled relation with their respective brackets, the end portions thereof are received in snugly fitting relation in the apertures in their respective brackets and the brackets are positioned adjacent the main portions of their respective caps. Further, the caps of cap and brackets assemblies of this type are generally secured together in assembled relation by welding. For use of a thermostatic switching device comprising a cap and bracket assembly of this type, the switching device is mounted so that the bracket thereof is disposed in thermal communication with other elements and/or the air in the surrounding area. Accordingly, when a temperature change occurs in the other elements and/or the air in the surrounding area with which the bracket is in thermal communication, a corresponding temperature change is produced in the bracket, and this temperature change is transmitted to the bimetallic disc of the switching device through the cap portion of the cap and bracket assembly. Hence, the bracket of a device of this type is operative for significantly reducing the response time of the device by providing enhanced thermal communication between the bimetallic disc of the device and other elements and/or the air in the surrounding area.
While the use of heat transfer brackets of the above described type has proven to be an effective means of reducing the response times of thermostatic switching devices, it has also been found that cap and bracket assemblies of the above described type are relatively expensive to manufacture and that in many instances even further reductions in the response times of thermostatic switching devices would be desirable. In this regard, heretofore it has generally been standard practice to secure the cap and bracket portions of assemblies of the above described type together by either resistance welding or ultrasonic welding. However, it has been found that the cap and bracket portions of assemblies of this type can only be effectively secured together by resistance welding when they are made of certain materials, such as stainless steel, and that often the use of these materials, particularly stainless steel, substantially increases the material costs of assemblies of this type. On the other hand, when the cap and bracket portions of assemblies of this type are made of aluminum, which has superior heat transfer qualities, they can only be effectively welded by ultrasonic welding. However, since ultrasonic welding is a comparatively expensive process, this also substantially increases the costs of cap and bracket assemblies of this type. Further, when the cap and bracket portions of assemblies of this tpe are welded together by ultrasonic welding, irregularities are often produced on the interior surfaces of the caps whereon bimetallic discs are supported when the cap and bracket assemblies are assembled in thermostatic switches. Unfortunately, it has been found that surface irregularities of this type can cause frictional resistance to the snap action or flexing movement of bimetallic discs and that this can significantly reduce the repeatability of switches. Finally, it has been found that when the cap and bracket portions of assemblies of this type are secured together by resistance welding or ultrasonic welding, they only contact one another at certain specific points, and this limits the heat transfer therebetween.
The instant invention provides an improved cap and bracket assembly for a thermostatic switch and a method of manufacturing same which overcome many of the disadvantages of the heretofore known cap and bracket assemblies and manufacturing methods. The cap and bracket assembly of the instant invention comprises a metallic cup-shaped cap having a substantially circular main portion and a substantially circular end portion and a metal bracket having an aperture therethrough which is received on the cap. More specifically, the bracket is assembled with the cup-shaped cap so that the reduced end portion of the cap is received in the aperture in the bracket and the end portion of the cap is crimped to capture the bracket in intimate engagement between the main portion of the cap and the end portion. The end portion of the cap preferably comprises a terminal end wall and an end portion side wall which extends from the main portion to the terminal end wall, and the end portion side wall is preferably dimensioned so that the extent thereof from the main portion to the end portion terminal end wall is at least three times the thickness of the bracket, or at least three times the thickness of that portion of the bracket which is adjacent the cap. Further, while the cap is constructed so that it has a certain amount of overall structural rigidity, the end portion of the cap is preferably formed so that the metal thickness thereof is at least thirty percent less than the metal thickness of the main portion of the cap to provide enhanced thermal communication between the bracket and a bimetallic disc received in the cap. The terminal end wall of the cap is preferably formed in a substantially flat configuration, and the main portion of the cap preferably comprises a main portion side wall and an intermediate end wall which extends inwardly from the main portion side wall to the end portion of the cap. When the cap is constructed in this manner, it is preferably assembled in the cap and bracket assembly so that the bracket is captured in intimate engagement between the intermediate end wall of the main portion and the terminal end wall of the end portion to provide uniform metal-to-metal contact between the cap and the bracket around the entire periphery of the cap.
The method of manufacturing a cap and bracket assembly in accordance with the instant invention comprises the steps of assembling a substantially circular metallic cap of the above described type with a bracket of the above described type so that the end portion of the cap is received in the aperture in the bracket, and crimping the end portion of the cap to capture the bracket in intimate engagement between the main portion of the cap and the end portion thereof. In the preferred form of the method, this step is carried out by axially compressing the end portion so that the bracket is captured in intimate engagement between the terminal end wall of the end portion and the intermediate end wall of the main portion and so that a substantially flat circular ring is provided in the interior of the cap for supporting a bimetallic disc thereon.
It is seen that the cap and bracket assembly of the instant invention and the method of manufacturing the cap and bracket assembly represent significant advancements over the heretofore available assemblies and manufacturing methods. Specifically, because the bracket is secured to the cap of the assembly by crimping the end portion of the cap to capture the bracket, intimate metal-to-metal contact between the cap and the bracket around the entire periphery of the cap is virtually assured so that enhanced thermal communication is provided between the bracket and a bimetallic disc received in the cap. Further, since the cap of the assembly is preferably formed so that the end portion thereof has a reduced wall thickness, thermal communication between the bracket and a bimetallic disc contained in the cap is even further enhanced. In addition, since the bracket is secured to the cap by crimping the end portion of the cap, a substantially flat, smooth circular ring is provided in the interior of the cap for supporting a bimetallic disc therein in a manner which permits the disc to flex freely and easily without significant frictional resistance from surface irregularities in the interior of the cap.
Accordingly it is a primary object of the instant invention to provide an improved cap and bracket assembly for a thermostatic switch.
Another object of the instant invention is to provide a cap and bracket assembly for a thermostatic disc wherein the bracket is secured to the cap by crimping the end portion of the cap to provide enhanced thermal communication therebetween.
Another object of the instant invention is to provide an economical method of manufacturing a cap and bracket assembly for a thermostatic switch.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.